In replacement of aromatic

The largest use of NMP is in extraction of aromatics from lube oils. In this appHcation, it has been replacing phenol and, to some extent, furfural. Other petrochemical uses involve separation and recovery of aromatics from mixed feedstocks recovery and purification of acetylenes, olefins, and diolefins removal of sulfur compounds from natural and refinery gases and dehydration of natural gas. 

Nucleophilic aromatic substitution of the anion from ary lace ton itrile 113 on the dichloroni-trobenzene 114 results in replacement of the para halogen and formation of 115. Reduction of the nitro group gives the corresponding aniline (116). Acylation of the amine with 3,5-diiodoacetylsa-licylic acid 117 by means of the mixed anhydride formed by use of ethyl chloroformate, gives, after alkaline hydroly.sis, the anthelmintic agent closantel (118) [28]. 

Also the bio-isosteric potential of the pyridazine system hitherto remained largely unexplored, despite the fact that several examples discussed in this review indicate that the replacement of aromatic moieties in bio-ac-tive compounds by the highly polar pyridazine nucleus may well improve the pharmacodynamic and/or the pharmacokinetic profile of a drug molecule. 

Hypophosphorous acW H3PO2 (M.W. 66.00), usually available as its 50% aqueous solution (density 1.274), is a specific reagent for replacement of aromatic diazonium groups by hydrogen under very mild conditions (at 0-25°) and in fair to good yields [288, 289] Procedure 46, p. 217). 

One of the most important challenges in the modern chemical industry is represented by the development of new processes aimed at the exploitation of alternative raw materials, in replacement of technologies that make use of building blocks derived from oil (olefins and aromatics). This has led to a scientific activity devoted to the valorization of natural gas components, through catalytic, environmentally benign processes of transformation (1). Examples include the direct exoenthalpic transformation of methane to methanol, DME or formaldehyde, the oxidation of ethane to acetic acid or its oxychlorination to vinyl chloride, the oxidation of propane to acrylic acid or its ammoxidation to acrylonitrile, the oxidation of isobutane to... 

Sodium fluoride does not effect any replacement of aromatic chlorine atoms with fluorine, unless they are activated by substitution of electron-withdrawing groups in the ring. Several examples are reported for heterocyclic compounds. 

This reaction has general utility for replacement of aromatic amino groups by hydroxyl groups. In contrast to the behavior of alkylamines, no rearrangements occur. 

Primary aromatic amines react with nitrous acid to give aryldiazonium ions, ArN2+, which are useful intermediates in synthesis of aromatic compounds. The process by which they are formed is called diazotization. The nitrogen in these ions can readily be replaced by various nucleophiles (OH, Cl, Br, I, CN). Diazonium ions couple with reactive aromatics, such as amines or phenols, to form azo compounds, which are useful as dyes. 

The replacement of aromatic amino groups by cyanide is easily accomplished by the action of cuprous cyanide on the diazonium compound (Sandmeyer). The procedure is illustrated by the preparation of o- and tolunitriles each is obtained in 64% to 70% yield. Several features are noteworthy. The diazonium solution is neutralized with sodium carbonate before treatment with cuprous cyanide solution so that the liberation of hydrogen cyanide is avoided. Also, vigorous stirring in the presence of an inert solvent is required during the addition of the cold neutralized diazonium solution to the cold cuprous cyanide solution so that the decomposition proceeds without violence. Methods for the preparation of cuprous cyanide have been described. ... 

With Br2 and FeBr3 (ionic conditions), electrophilic aromatic substitution occurs, resulting in replacement of H by Br on the aromatic ring to form ortho and para isomers. 

The Bucherer reversible reaction of conversion of naphthols to anilines by aminolysis is of outstanding importance in naphthalene chemistry. The reaction is used for the replacement of aromatic amino groups by hydroxy groups, in the naphthalene series. The reaction is valuable in the synthesis of naphthalene dye intermediates and may be represented as follows ... 

Metalating agent. n-Butyllithium is one of the most useful agents for the replacement of aromatic hydrogen in ethers, usually ortho to the ether function tetrahydro-furane is generally preferred as solvent, but ether is often used. For example, 1,7-dimethoxynaphthalene yields the 6-Li derivative, convertible into the corresponding methyl and carboxy compounds. ... 

It would appear, therefore, that all of the products identified in the vapor-phase radiolyses could be formed from excited molecules. Some products, however, are so much more abundant in vapor-phase radiolysis than in photolysis or liquid-phase radiolysis as to suggest the likelihood of additional precursors. In particular, the formation of acetylene, the isomerization of the xylenes, and the replacement of aromatic hydrogen by methyl groups are difficult to explain solely in terms of reactions of excited molecules. 

The products resulting from replacement of aromatic H by CH3, in the vapor-phase radiolyses of the alkylbenzenes, show a strong preference for meta orientation. That these products are derived from radicals is suggested by our observation that no xylenes are formed when toluene vapor is radiolyzed in the presence of iodine. The distribution of isomers does not, however, correspond to the preferential ortho substitution found (16) in the homolytic methylation of toluene, nor does it resemble the nearly statistical distribution observed in liquid phase radiolysis or in vapor-phase photolysis at 2537 A. (17). The process is obviously complex, and there is little direct evidence on which to base a mechanism. It may, nevertheless, be of interest that the C8H9+ ion is observed (15) in the mass spectrum of toluene at moderate pressures. Neutralization of such an ion could lead to radicals and ultimately to aromatic products. It is also of interest that the high pressure mass spectrum shows (15) abundant formation of dimeric ions, which may well be involved in the enhanced production of dimer and higher polymeric products in the vapor phase radiolysis. 

The alcohols are employed to effect the replacement of aromatically bound halogen atoms by heating in the presence of an alkali. In this way, p-nitrophenetole and o-nitroanisole are made by treating p-nitro-chlorobenzene with ethanol and o-nitrochlorobenzene with methanok ... 

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